Mercurial > octave
view scripts/image/cubehelix.m @ 23084:ef4d915df748
maint: Merge stable to default.
author | John W. Eaton <jwe@octave.org> |
---|---|
date | Mon, 23 Jan 2017 14:27:48 -0500 |
parents | 3a2b891d0b33 e9a0469dedd9 |
children | 092078913d54 |
line wrap: on
line source
## Copyright (C) 2014-2016 Carnë Draug ## ## This file is part of Octave. ## ## Octave is free software; you can redistribute it and/or modify it ## under the terms of the GNU General Public License as published by ## the Free Software Foundation; either version 3 of the License, or ## (at your option) any later version. ## ## Octave is distributed in the hope that it will be useful, but ## WITHOUT ANY WARRANTY; without even the implied warranty of ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ## GNU General Public License for more details. ## ## You should have received a copy of the GNU General Public License ## along with Octave; see the file COPYING. If not, see ## <http://www.gnu.org/licenses/>. ## -*- texinfo -*- ## @deftypefn {} {@var{map} =} cubehelix () ## @deftypefnx {} {@var{map} =} cubehelix (@var{n}) ## Create cubehelix colormap. ## ## This colormap varies from black to white going though blue, green, and red ## tones while maintaining a monotonically increasing perception of intensity. ## This is achieved by traversing a color cube from black to white through ## a helix, hence the name cubehelix, while taking into account the perceived ## brightness of each channel according to the NTSC specifications from 1953. ## ## @example ## rgbplot (cubehelix (256)) ## @end example ## ## The argument @var{n} must be a scalar. ## If unspecified, the length of the current colormap, or 64, is used. ## ## Reference: Green, D. A., 2011, ## @cite{"A @nospell{colour} scheme for the display of astronomical intensity ## images"}, Bulletin of the Astronomical Society of India, 39, 289. ## ## @seealso{colormap} ## @end deftypefn ## Author: Carnë Draug <carandraug@octave.org> function map = cubehelix (n = rows (colormap ()), start = 0.5, rots = -1.5, hue = 1, gamma = 1) if (nargin > 5) print_usage (); elseif (! isscalar (n)) error ("cubehelix: N must be a scalar"); endif n = double (n); if (n > 1) coeff = [ -0.14861 -0.29227 1.97294 1.78277 -0.90649 0.00000]; fract = ((0:n-1) / (n-1))'; angle = 2 * pi * (start/3 + 1 + rots*fract); fract .^= gamma; amp = hue * fract .* (1-fract) /2; map = fract + amp .* ([cos(angle) sin(angle)] * coeff); ## Clip values (only in case users have changed values of hue or gamma) map(map < 0) = 0; map(map > 1) = 1; elseif (n > 0) map = [0, 0, 0]; else map = zeros (0, 3); endif endfunction ## A better demo of this colormap would be a 3D plot in NTSC instead of ## RGB values. That would really show what this colormap is about. %!demo %! ## Show the 'cubehelix' colormap profile and as an image %! cmap = cubehelix (256); %! subplot (2, 1, 1); %! rgbplot (cmap, "composite"); %! subplot (2, 1, 2); %! rgbplot (cmap);